1. Field of the Invention
The present invention relates to a polarization beam splitting element that splits an entering beam according to polarization directions, and particularly to a polarization beam splitting element that is constituted by a wire grid (one-dimensional grating structure) having a grating period smaller than a wavelength of the entering beam and a multi-layered dielectric film layer.
2. Description of the Related Art
A wire grid that is a one-dimensional grating structure formed of a metal and having a grating period smaller than a wavelength (also referred to as a “use wavelength”) of an entering beam has a function of splitting beams whose polarization directions are mutually different. Japanese Patent Laid-Open No. 2003-502708 discloses a wire grid having a visible wavelength-order minute grating period and formed on a substrate.
Such a wire grid is generally designed to reflect s-polarized light and transmit p-polarized light. However, in fact the wire grid reflects part of the p-polarized light to be transmitted therethrough, which deteriorates its beam splitting characteristic and light utilization efficiency.
Thus, Japanese Patent Laid-Open No. 2008-523422 discloses a wire grid polarization beam splitting element in which a layer formed by laminated dielectric thin films or by laminated dielectric grids is disposed at an interface between a wire grid and a substrate or an entrance medium, for the purpose of suppressing reflection of p-polarized light. Moreover, Japanese Patent Laid-Open No. 2003-519818 discloses a wire grid polarization beam splitting element that is used by being sandwiched between transparent substrates or prisms, for the purpose of suppressing generation of astigmatism at the substrate and of improving handling easiness of grating.
However, the polarization beam splitting elements disclosed in Japanese Patent Laid-Open Nos. 2003-502708, 2008-523422 and 2003-519818 require increase of a grating thickness of the wire grid in order to achieve a sufficiently high reflectance for s-polarized light, which causes the wire grid to absorb the p-polarized light to be transmitted.
Moreover, the wire grid polarization beam splitting element that is used by being sandwiched between the transparent substrates or prisms can suppress the generation of the astigmatism by the substrate, but has a higher reflectance for the p-polarized light as compared with a case where an air or vacuum space is formed on a beam entrance side of the wire grid.